You'll generally find that backing stuff up is a lot more twitchy than running with the locomotive pulling it. I'm still learning the paths through the Ross Double-Slip Switches, I occasionally set them wrong for the path intended and boom, another derailment!
Yes... to every word. The backing up seems to be related to weight as does the 2.2% graded curve (O-54)... the string effect on the light rolling stock lifts the wheels off the outside rail once there are around nine or ten cars in the consist. I stuck some steel bar in a few of them and it seems to have ended that issue. The paths! Oh Yes! the paths.